Process for improving fatty acids



United States Patent 3,471,536 PROCESS FOR IMPROVING FATTY ACIDS Jean Klere, Colombes, and Roger Gadefaix, Issy-les- Moulineaux, France, assignors to Lever Brothers Company, New York, N.Y., a corporation of Maine No Drawing. Filed Dec. 19, 1966, Ser. No. 602,560 Claims priority, application France, Dec. 29, 1965, 44 209 rm. or. the 1/08 US. Cl. 260419 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for improving the quality of fatty acids, in particular fatty acids that can be used for the preparation of soap.

Edible oils and fats (referred to hereafter as glyceride oils) in the crude state always contain a certain amount of free fatty acid which has to be removed to prepare a neutral glyceride oil which can be used for the preparation of fatty foodstuffs. The most common method of removing the fatty acid is by alkali-refining in which the crude glyceride oil is neutralised with aqueous alkali, for instance caustic soda. The resulting aqueous phase, commonly known as soap stock, is separated from the neutral glyceride oil by decantation or centrifugation, and contains the neutralised free fatty acid as well as other impurities and a small amount of glyceride oil. In order to recover the fatty acid from the soap stock, the latter is acidified, for example, with sulphuric acid, and the precipitated acid oil is separated. The acid oil is usually subjected to a further treatment to hydrolyse the glycerides still present into fatty acid and glycerol, and this is normally carried out by heating the acid oil to a high temperature in an autoclave in the presence of water. In order to purify the fatty acid still further, the separated acid is then distilled to separate volatile acid from nonvolatile impurities which are concentrated in a residual fraction. The acid thus obtained is commonly called a technical fatty acid.

The distillation process can be modified to prepare, for example, specific fractions containing fatty acid of a certain chain length or in which highly volatile constituents are removed which are not very stable and affect soap made from the fatty acid.

When the technical fatty acid is to be used in the manufacture of toilet soap it is important to obtain from the crude fatty acid a high proportion of a fraction which is suitable for the preparation of good quality soap. In addition to free fatty acid, mucilage and colouring material, the crude vegetable or animal glyceride oils from which technical fatty acids are prepared also contain small proportions of impurities which can be generally designated by the terms oxidation products, oxidised fatty acids, and carbonyl derivatives, which generally result from the action of oxygen on the free fatty acids or on the oils. These contaminants are characterised by the presence of compounds such as peroxides, epoxides, aldehydes and ketones, and they accumulate in the by-products of the refining operation of glyceride oils, especially in the soap stock and the acid oil. Their presence in technical fatty 3,471,536 Patented Oct. 7, 1969 ice acid used for soap manufacture is very undesirable, for they give rise to coloured compounds which affect the appearance of the final product. These impurities complicate the process of purification of the fatty acid, especially by distillation, so that the preparation of fatty acid of satisfactory purity meets with many difficulties. One can try to purify the acid before the distillation by treating it, for example, with oxidising agents, such as a hypochlorite, a permanganate or even ozone, as well as by treating it with adsorption agents, such as silica gel, active carbon and a bleaching earth. However, owing to the corrosive nature of the oxidising agents, costly apparatus is required in order to put these processes into practice. When using adsorption agents it is not only the impurities that are adsorbed but also a considerable amount of fatty acid, which is thus lost.

It has now been found that the quality of the fatty acid which is used for the preparation of soap can be considerably improved by treating it with a small amount of an amino compound that is a hydrazine having a free amino group or is a primary aliphatic amine of from 12 to 18 carbon atoms in the molecule, and by this means the above disadvantages can be avoided. Although the effect of the process of the invention cannot be fully explained, it is supposed that the removal of undesirable impurities is due to the combination of two types of reaction, namely the reduction of the oxidation products without the saturation of olefinic bonds of the unsaturated fatty acids, and the chemical fixation reaction of the remaining oxidation products, resulting in conversion to separable reaction products, the final result being a practically complete elimination of the oxidation products.

Accordingly, the invention provides a process for improving a fatty acid containing impurities giving rise to colour instability when soap is made from it, in which the fatty acid is contacted with an amino compound that is a hydrazine having a free amino group or is a primary aliphatic amine of from 12 to 18 carbon atoms in the molecule, and reaction products of the amino compound and the impurities are subsequently removed. Preferably the reaction products are removed by distillation of the fatty acid.

The amino-compounds to be used can be generally represented by the formula R-NH in which R represents either an amino group in which one or both of the hydrogen atoms can be replaced by substituted or unsubstituted aliphatic or aromatic hydrocarbon radicals, especially substituted or unsubstituted alkyl, cycloalkyl or aryl groups, or R represents an aliphatic hydrocarbon radical containing from 12 to 18 carbon atoms, which can be saturated or unsaturated. The amino compounds of the first group are hydrazine and its monoand di-substitution derivatives, for instance phenylhydrazine, while the compounds of the second group are primary aliphatic amines, especially alkylamines, for instance stearylamine and lauryla-mine, and alkenylamines, for instance oleylamine. Hydrazine can be used in hydrated form, for instance as an aqueous solution of 20 to 30% concentration. Preferably the hydrazine compound contains from 1 to 30 carbon atoms, and especially from 1 to 15 carbon atoms in the molecule. A preferred group of amino compounds are those selected from the group consisting of hydrazine, phenylhydrazine and primary aliphatic amines having from 12 to 18 carbon atoms.

The improvement of the quality of the fatty acids can be effected by stirring the fatty acid to be treated with a small quantity of the amino compound at a temperature which can be adapted to the type of fatty acid as well as to the type of amino compound. The amount of amino compound which is suitable depends on the conditions of treatment and the type and quality of the fatty acid to be treated, but in general it is between 0.01 and 5% by weight of the fatty acid to be treated, the best results being obtained when the amount of amino compound is between 0.05 and 1% by weight. It is preferable to combine the treatment with the distillation process itself. Preferably therefore the fatty acid and the amino compound are brought together at a temperature substantially below the decomposition temperature of the amino compound, and the temperature of the acid is then raised to boiling point, as in distillation. Preferably the fatty acid is contacted with the amino compound at a temperature of from 40 to 160 C., and especially from 50 to 90 C. Conveniently the temperature of the fatty acid is then progressively increased until the distillation temperature, normally between 180 and 250 C., is reached. During this treatment at relatively high temperatures part of the amino compound which does not combine with the carbonyl groups present in the impurities in the fatty acid probably decomposes and reduces the fatty acid oxidation product impurities. The oxidation products that are chemically combined with the free amino group of the amino compound are substantially removed during distillation, while the reduced oxidation products are harmless and can be left in the final product.

The above procedure has the advantage that by combining the contacting step with the distillation it is not necessary to introduce a separate treatment step in the preparation of high-quality fatty acids suitable for the production of stable soaps. Even acid materials of inferior quality that are unsuitable for the preparation of soaps, can be improved by the process of the invention. Such acid materials comprise, for example, the product obtained by distilling the hydrolysed residue from the first distillation of crude fatty acid. Such a material is unsuitable for the preparation of soaps because soaps made starting with it become rapidly coloured, but when it is re-distilled in the presence of a small amount of the amino compound, a fatty acid can be obtained in a yield of about 80-90%, that can immediately be used for the preparation of stable soaps.

The process of the invention can also be carried out after the normal distillation used in making technical fatty acids, but it is then necessary to remove substantially the reaction products of the oxidation products and the amino compounds, which can be done by agitating the treated fatty acids with a small amount of a bleaching earth at a temperature below 100 0., followed by filtration. Active carbon or silica gel in amounts of between 1 and 3% can also be used.

The following examples illustrate the invention.

Example 1 To a crude fatty acid of groundnut oil, obtained by hydrolysis of an acid oil obtained as a by-product during the neutralisation of crude groundnut oil with caustic soda, was added 0.4% by weight of a 24% aqueous solution of hydrazine hydrate; the mixture Was stirred at 60 C. and subjected to distillation under normal conditions used in the production of a technical fatty acid. The temperature during the distillation was 225-230 C., the pressure 3-4 mm. of mercury and a conventional vacuum distillation column (Lurgi column) Was used, the fatty acid being introduced in the middle of the column after preliminary heating. The residue was recovered at the bottom and the improved fraction was recovered in the upper part of the apparatus, the distillation treatment being continued until the yield of the upper fraction was 80%. The acid obtained was converted to soap with potassium hydroxide.

The colour of the soap was determined by means of a spectrophotometer (Jobin Yvon type) at a wave length of 470 millimicrons with a cell of 4 cm., using a 5% aqueous alcoholic solution of the soap.

The optical density was determined as a measure of the colour of the soap, a value of about 0.200 indicating that the fatty acid is unsuitable for the preparation of soap while a value below 0.100 generally indicates an excellent quality of fatty acid.

The presence of carbonyl compounds in the treated fatty acid Was determined by thin layer chromatography. The adsorbent used was silica gel G, the film had a thickness of 250 microns and was activated for 2 hours at a temperature of 110 C. The mobile phase consisted of a mixture of light petroleum and ether (20%), containing a small amount of acetic acid, and the elution front was 15 cm. long. The chromatogram was treated with a 0.4% solution of 2,4-dinitrophenylhydrazine in 2 N hydrochloric acid in order to develop any spots due to the presence of carbonyl compounds: such spots have a yellow, orange or yellow-orange colour.

The groundnut oil fatty acid treated as described above gave a soap of colour 0.080 and no carbonyl compounds were detected. The distillation process was repeated Without using the hydrazine and the final product had a soap colour of 0.100 and was shown to contain carbonyl compounds.

Example 2 A crude coconut oil fatty acid obtained by the alkalirefining process was contacted under the same conditions as in Example 1 with 0.4% by weight of a 24% aqueous solution of hydrazine hydrate, and the product distilled to a yield of 80%, converted to soap and tested as before. The soap colour was 0.060 and no carbonyl compounds were detected. The same fatty acid which had been submitted to the normal distillation up to a yield of 80% without using hydrazine gave a soap of colour 0.120 and the presence of carbonyl compounds was detected.

Example 3 A crude fatty acid of groundnut oil obtained by the alkali-refining process was treated as described in Example l, but using 0.3% by weight of phenylhydrazine instead of the hydrazine hydrate, and the product converted to soap and tested as before. The soap had a colour of 0.090 and no carbonyl compounds were detected. The process was repeated without the use of phenylhydrazine; the product gave a soap of colour 0.120 and carbonyl compounds were detected.

Example 4 A coconut oil fatty acid obtained by hydrolysis of the residue of the distillation of a technical coconut oil fatty acid was treated as in Example 1, but using 0.5% by weight of a 24% aqueous solution of hydrazine hydrate, and continuing distillation to a yield of and soap was prepared and tested as before. The colour of the soap obtained was 0.100, while the colour of the soap obtained with the fatty acid distilled without the hydrazine treatment was 0.450. The first product did not contain carbonyl compounds, while the second product gave carbonyl spots on the chromatogram.

Example 5 A crude coconut oil fatty acid obtained by acid hydrolysis of an acid oil was distilled in the presence of 0.1% of hydrazine by weight under the same conditions as described in Example 1, except that distillation was continued to a yield of 85 and the product was converted to soap and tested as before. The colour of the soap was 0.070. The same material distilled without hydrazine treatment gave a soap of colour 0.100 and showed traces of carbonyl compounds, which were absent from the product obtained using hydrazine.

Example 6 A groundnut oil fatty acid obtained by hydrolysis of residual fatty material from a distillation of a technical fatty acid, was contacted with 0.1% by weight of hydrazine, distilled, and converted to soap which was tested, all as in Example 1. The colour of the soap was 0.040, and no carbonyl compounds were detected; when the same material was treated without hydrazine, the colour of the soap obtained was 0.700, and the soap showed traces of carbonyl compounds.

Example 7 A crude groundnut oil fatty acid obtained by hydrolysis of an acid oil was treated with 0.6% by weight of laurylamine and distilled, converted into soap, and the soap tested as in Example 1. The colour of the soap obtained was 0.065, while the same fatty acid distilled without addition of laurylamine gave a soap of colour 0.150.

Example 8 A crude coconut oil fatty acid obtained by the alkalirefining process is distilled to a yield of 80% and to the distillate at 75 C. is added 0.1% by weight of hydrazine hydrate. The mixture is stirred and 1.5% by weight of active carbon is added and the mixture again stirred. The active carbon is then removed by filtration, leaving an acid of improved quality for soap manufacture.

What is claimed is:

1. A process for improving a fatty acid containing impurities giving rise to color instability when soap is made from it Which comprises contacting the fatty acid with from 0.01 to 5% of its Weight of an amino compound selected from the group consisting of hydrazine, phenylhydrazine and a primary aliphatic amine having from 12 to 18 carbon atoms, and removing the fatty acid from the reaction products of the amino compound and the impurities.

2. A process according to claim 1, in which the amino compound is hydrazine.

3. A process according to claim 1, in which the amino compound is phenylhydrazine.

4. A process according to claim 1, in which the amino compound is a primary alkylamine of from 12 to 18 carbon atoms.

5. A process according to claim 1, in which the amino compound is laurylamine, stearylamine or oleylamine.

6. A process according to claim 1, in which the fatty acid and the amino compound are brought together at a temperature below the decomposition temperature of the amino compound and the temperature of the acid is then raised to boiling point.

7. A process according to claim 6, in which the reaction products are removed by distillation of the fatty acid.

8. A process according to claim 1, in which the fatty acid is contacted with the amino compound at a temperature of from to 160 C.

9. A process according to claim 8, in which the fatty acid is contacted with the amino compound at a temperature of from to C.

10. A process according to claim 1, in which the fatty acid is contacted with from 0.05 to 1% of its weight of amino compound.

11. A process according to claim 1, in which the fatty acid is one which has been obtained by the hydrolysis of an acid oil from a soap stock prepared by alkali-refining a crude glyceride oil.

12. A process according to claim 11, in which the fatty acid is one which has been obtained by the distillation of a hydrolysed acid oil from a soap stock prepared by alkali-refining a crude glyceride oil.

References Cited UNITED STATES PATENTS 2,126,334 8/1938 Langedijk et al 260-425 2,581,452 1/ 1952 Solomon 260-419 2,664,430 12/1953 Reinish et al 260-415 ALEX MAZEL, Primary Examiner R. V. RUSH, Assistant Examiner 

